JPH03104778A - Control method for full electric power steering device - Google Patents

Abstract

PURPOSE:To suppress the cost resulting from provision of sensor and eliminate increase of the man-hours for the same purpose by calculating the thrust force of the rack shaft of a gear box, controlling the output of a motor with this thrust force, and thereby eliminating a thrust force sensor. CONSTITUTION:A torque signal (a) is entered into an A/D conversion part 4a of a CPU 4, while a car speed signal (b) is input directly to a CPU 4. From the signals (a), (b) the CPU 4 determines a rack thrust force value (c) as a command value from a map of the rack thrust force vs. torque, gives it to a D/A converter 5, and emits a right signal (d) and a left signal (e) for determination of the motor rotating direction. An analogous rack thrust force value 5c given by this D/A converter 5 is compared by a comparator 6 with a rack thrust force value 25c which was fed from a rack shaft thrust force sensor 25 via a filter 25a and an amplifier 25b. When the value 5c is greater than the value 25c, a signal of '1' is given from an And circuit 7, and a driver part 9 drives a transistor 14 while another driver part 12 drives a transistor 17. Thus the motor 18 is rotated to the right.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for controlling the output of an assist motor of an all-electric power steering system. [Prior art] In the conventional M'S method for assist motor output,
In order to prevent the steering wheel from returning poorly due to attenuation of the restoring force from the steering wheel when returning the steering wheel, the steering wheel side torque sensor and the external force from the road surface are detected by the steering gear side torque sensor and the steering assist force by the motor is controlled. Was. This can be seen, for example, in JP-A No. 6
3-301173. [Problems to be Solved by the Invention] As mentioned above, the conventional method for controlling the output of the assist motor requires a sensor that detects the equivalent of an external force from the road surface, resulting in high costs, increased man-hours for installation, etc. was occurring.

The present invention has been made in view of these points, and its purpose is to output the force that overcomes the friction force between the tires and the road surface as the steering force of the vehicle as a thrust force of the rack shaft, and to detect this thrust force. The purpose of this invention is to obtain a control method for an all-electric power steering system that does not require sensors or the like as a means for controlling the power steering system. [Means for Solving the Problems] In order to achieve the above object, the present invention calculates the thrust of the rank shaft of the gear box, and controls the output of the assist motor using this thrust. It is.

[Effect]

In the control method according to the present invention, the thrust of the rack shaft is calculated from an equation related to torque.

〔Example〕

FIG. 4 is a circuit diagram showing an all-electric power steering system in which a rank axis sensor or the like is used. In the figure, ■ indicates the handle torque T. 2 is a filter for removing the noise of the torque signal a and the resonance frequency of the system, 3 is a vehicle speed sensor that outputs a vehicle speed signal b, 25 is a rack shaft thruster sensor, and 25a is a filter , 25b is an amplifier, and 4 is C that controls the entire circuit.
PU, 4a is an A/D converter of the CPU 4, 5 is a D/A converter, 6 is a comparator, 7, 8 are AND circuits, 9-12 are drive units, l3 is a power switch means such as a relay, 14- l7
18 is a transistor connected to the drive units 9 to 12, 18 is an assist motor, 1920 is a resistor for detecting motor current,
21 is a current detector that outputs the current value 9 of the assist motor 18, 22 and 23 are analog switches, 24 is a buffer that outputs the inter-terminal voltage value vM of the assist motor 18, and BT is a battery.

Next, the general operation of the circuit shown in FIG. 4 will be explained. The torque signal a is input to the A/D converter 4a of the CPU 4,
The vehicle speed signal b is directly input to the CPU 4. CPU4 is
From the signals a and b, the rack thrust value C as a command value is determined from the map of rack thrust FR versus torque T'st in FIG. d, outputs the left signal e.

In addition, in Figure 5, S represents the vehicle speed, ! = Q −*
St = l - e 3 = 'l, and as the value increases, the vehicle speed increases. If the vehicle is far-reaching, the assist force will be small and the steering wheel will be heavy.

The analog rack thrust value 5c outputted from the D/A converter 5 is compared with the rack thrust value 25c manually inputted from the rank axis secondary force sensor 25 via the filter 25a and the amplifier 25b by the comparator 6, and the value 5C is obtained. If is larger than the value 25c, it outputs "1" to the AND circuit 7.8, and if it is smaller, it outputs rOJ. Here, if the CPU 4 is outputting a right signal d of "1" and a left signal e of "0", the value 5
If C is greater than the value 25c, the AND circuit 7 outputs “
1'' signal is output, and the drive unit 9 drives the transistor 14. Further, the drive unit l2 directly inputs the right signal d from the CPU 4 and drives the transistor l7. Therefore, current flows from left to right in the motor 18, causing the motor 18 to rotate in the right direction. If the value 5C is less than the value 25c,
Alternatively, if both the right signal d and the left signal e are "0", neither transistor is driven.

In the case of clockwise rotation, the analog switch 22 is turned on, and the voltage at the left end of the motor is inputted to the CPU 4 via the bath sofa 24. At this time, the voltage at the right end of the motor 18 is approximately close to the body potential of the vehicle body, and therefore the voltage at the left end of the motor 18 is approximately the motor end voltage. In the case of counterclockwise rotation, the analog switch 23 is turned on and the same operation is performed.

FIG. 1 is an explanatory diagram schematically showing a steering system.

In the figure, 1 is a torque sensor that detects the handle torque T'st, 18 is an assist motor, 26 is a pinion shaft with an effective radius R, and 26a is ? 27 is the rank shaft where the thrust force FII appears, F is the force in the direction perpendicular to the rank tooth surface that the pinion teeth act on the rack teeth, and 28 is the wheel.

In such a steering system, the following equation holds.

Tst+T. o=J-d"θ/dt"+D-dθ
/dt+F■+F (sinαX[J.+cosα
xtl. ) X RP・ ・ ・ ・(1) ? a=F 0 cos α-U,...l (2) Here, T. 4. is the motor output torque, which is calculated from the motor current value ■8 using the graph shown in Figure 2. J and D are the inertia and viscosity of the gear box system, and are equivalent values to the pinion shaft 26. θ is Binion axis 2
6 angle, F■ is the friction of the steering system, α is the pressure angle of the rack teeth, Up is the friction coefficient of the pad part of the rank shaft 27, U
g is the friction coefficient of the holder portion of the rank shaft 27.

(The following equation (3) is obtained from equation 11.

F= (Tst+T.4o J-d"θ/d1-D
-dθ/dt-F■) / (sinαxU, +cosαXU,) X R1
(3) F can be found by finding the angular acceleration dtθ/dt'' and angular velocity dθ/dt of the binion shaft 26 and substituting these values into the above equation (3), which can be expressed as (2
) thrust force F8 of the rack shaft can be obtained. This makes it possible to control the motor assist force in the same manner as in the prior art.

The angular acceleration dtθ/dt" and the angular velocity dθ/dt of the pinion shaft 26 are determined as follows. Motor terminal voltage is VM% rotor resistance R, motor current IH% rotation speed is Φ
, when the motor constant is K, the following equation holds. VPl=R IM+K4) ・・・・・・(31.゛.Φ
=(vo-RI,1)/K...{4}If the reduction gear ratio is N, dθ/dt=(Φ/N)...(5) d2θ/d
t"=d(Φ/N)/d t (6) In this way, dθ/dt and dtθ/d t" can be obtained. Next, an example of the value of each constant is shown in the table.

FIG. 3 shows an embodiment of the control method when the thrust of the rack shaft is calculated by calculation as described above. In FIG. 3, the same or equivalent parts as in FIG. 4 are given the same reference numerals. In FIG. 3, the output signal f from the CPU 4 is the thrust of the rank axis determined by calculation. As can be seen from FIG. 3, this embodiment not only eliminates the need for a sensor, but also simplifies the circuit, compared to FIG. 4, which uses a sensor. [Effects of the Invention] As explained above, the present invention calculates the thrust of the rack shaft of the gear box and controls the output of the assist motor using this thrust, thereby eliminating the need for a thrust sensor.
This has the effect of eliminating high costs due to sensors, increased man-hours for sensor installation, etc. It also has the effect of eliminating noise that was previously generated by sensors.

[Brief explanation of drawings]

Claims (1)

[Claims] An all-electric power steering device that performs steering using steering assist force from a motor, characterized in that the thrust of a rack shaft of a gear box is calculated, and the output of the motor is controlled by this thrust. Control method for the extraction device.